DDG: Enable code-reloading.

This is the first fully working version.  Depends on minor changes to
DDG to allow for multiple reloads.
DDG: clean up messaging a bit.

I'm not so excited about the repeated line but I can't think of a better
way just yet.
DDG: vaguely improve efficiency.

This reduces the number of times we actually rebuild the blocks.  It
makes a slightly perceptible difference in the speed of response.
DDG: notice removed classes, as well.

This is probably a pretty niche need, but making it work in order to
complete the cycle.